Direct and simultaneous determination of 5-aminolaevulinic acid and porphobilinogen in urine by hydrophilic interaction liquid chromatography-electrospray ionisation/tandem mass spectrometry

Urinary concentrations of 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG) are elevated in patients with acute hepatic porphyrias, especially during acute attacks. Current assays require lengthy sample pre-treatment and derivatisation steps. We report here a rapid, sensitive and specific hydrophilic interaction liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, for the direct and simultaneous quantitation of ALA and PBG in urine following simple dilution with acetonitrile and centrifugation prior to injection. ALA and PBG were detected using selected reaction monitoring mode, following positive electrospray ionisation. Urine samples (N?=?46) from active and latent mutation-confirmed acute hepatic porphyria patients and normal subjects (N?=?45) were analysed and the results compared with those of a commercially available spectrophotometric method. The validated calibration range was 3-3000?μmol/L for ALA and 2-2000?μmol/L for PBG. For both analytes, imprecision (relative standard deviation) was less than 5% and accuracy (percentage nominal concentrations) was between 88 and 109%. The lower limit of quantitation was 0.1 μmol/L for both analytes. The calculated LC-MS/MS and spectrophotometric results from patient samples compared well [Pearson correlation (r2) of 0.99 and 0.95, for ALA and PBG, respectively]. The method was successfully applied to the measurement of ALA and PBG in urine samples for the screening, biochemical diagnosis and treatment monitoring of patients with acute hepatic porphyrias.     

Characterization of the radiation shielding properties of US and Russian EVA suits using passive detectors

Radiation measurements using passive detectors were carried out to assess the shielding properties of the US Extravehicular Mobility Unit (EMU) space suit and the Russian Orlan-M suit during irradiations of the suits and a tissue-equivalent phantom by monoenergetic proton and electron beams at the Loma Linda University Medical Center (LLUMC). During irradiations of 6 MeV electrons and 60 MeV protons, absorbed dose as a function of depth was measured using thermoluminescent detector (TLD) exposed behind swatches of the two suit materials and inside the two extravehicular activity (EVA) helmets. Considerable reduction in electron dose was measured behind all suit materials on exposure to 6 MeV electrons. Slowing of the proton beam in the suit materials led to an increase in dose measured on exposure to 60 MeV protons. During 232 MeV proton irradiations, measurements were made with TLD and CR-39 plastic nuclear track detector (PNTD) at five organ locations inside a tissue-equivalent phantom, exposed both with and without the two EVA suits. The EVA helmets produced a 13% to 27% reduction in total absorbed dose and a 0% to 25% reduction in dose equivalent when compared to measurements made in the phantom head alone. Differences in absorbed dose and dose equivalent between the suit and non-suit irradiations for the lower portions of the two EVA suits tended to be smaller. Proton-induced target fragmentation was found to be a significant source of increased dose equivalent, especially within the two EVA helmets, and average quality factor inside the EMU and Orlan-M helmets was 2% to 14% greater than that measured in the bare phantom head.     

Application of the optically stimulated luminescence (OSL) technique in space dosimetry

This paper reviews the state of the optically stimulated luminescence (OSL) technique for space dosimetry applications, focusing on the properties of carbon-doped aluminum oxide (Al₂O₃:C). New data presented include the most complete and recent values for the relative efficiency η_HCP,γ for heavy charged particles as a function of the incident radiation's linear energy transfer (LET), obtained through ground-based experiments at heavy ion accelerators. We also discuss the factors influencing the OSL efficiencies, the LET-dependent properties of Al₂O₃:C, and the experience gained from past space experiments using Al₂O₃:C. The characterization of the OSL efficiency values as a function of LET allows the use of the OSL of Al₂O₃:C in combination with plastic nuclear track detectors for personal dosimetry of astronauts, as proposed by the NCRP Report 142.     

The growth of a single crystal of Sr3CuIrO6 and its magnetic behavior compared to polycrystals

We have grown single crystals of the psuedo-one-dimensional compound Sr₃CuIrO₆, a K₄CdCl₆-derived monoclinic structure with Cu-Ir chains along the [101] direction. We present the ac and dc magnetization behavior of the single crystals in comparison with that of the polycrystalline form reported earlier. There is a distinct evidence for at least two magnetic transitions, at 5 K (T ₁) and 19 K (T ₂), with different relative magnitudes in the single and polycrystals. The low temperature magnetic relaxation behavior of both the forms is found to be widely different, exhibiting unexpected time dependence.     

Safety Stock and Service Levels in Periodic Review Inventory Systems

The management of requirement (purchased parts and components) uncertainty in MRP systems is a serious problem for manufacturing firms. When manufacturing service levels fall below a predetermined service level, safety stock must be increased in order to adjust to the competitive environment. This paper presents the results of a set of simulation experiments in which we investigate some of the complexities of safety stock requirements, lot sizing performance and the marginal safety stock requirements associated with various service level policies. The results of the experiments have empirically shown that the marginal units of safety stock required for various service level policies follow a predictable (measurable) pattern. The research also indicates that the economic advantages of well-known dynamic lot sizing procedures are diminished by the presence of requirements uncertainty. Another important finding is the interaction between service level and ‘lumpy’ requirements. High levels of the coefficient of variation and the economic time between orders resulted in larger orders, reduced safety stock and high service levels. In general, the overall findings from this research will hopefully provide the decision maker with an in-depth understanding of the measurement and impact of various service level policies.